PEM fuel cells (PEMFCs) generate power from electrochemical conversion of fuels such as hydrogen and hydrocarbons at its anode and oxidants such as oxygen and air at its cathode using a membrane as electrolyte. The membrane acts both as a proton conductor and a barrier between the fuel and oxidants. Developing a membrane with high ionic conductivity at high temperature and low relative humidity (RH %) is desired to simplify the humidification system and operation, improve fuel cell performance, and reduce the cost for early commercialization of fuel cell electric vehicles. Current state-of-the-art membranes such as Nafion™ membranes and other perfluorosulfonic acid (PFSA) membranes have reasonable conductivity at high RH % and at temperatures below 100° C. However, these membranes hold less water at low RH % and undergo permanent thermal degradation at temperatures above 100° C.
In these membranes, conductivity at low RH % could be improved by increasing the acid content (—SO3H group) or by reducing the equivalent weight (EW). However, increasing the acid content beyond certain values leads to polymer dissolution, weak mechanical structure, and eventually failure of the membrane in fuel cells. The linear-chain-structure in current state-of-the-art PFSA membranes is inadequate to allow acid content beyond certain values. Without increasing the acid content and preventing polymer structure damage at high temperature, current state-of-the-art PFSA membranes are unable to function at low RH % and at high temperature. In addition, these current PFSA membranes are manufactured under extremely high reaction conditions using sophisticated equipment and processes that make them difficult and expensive to produce.